Antibodies to nucleic acids in patients with systemic lupus erythematosus and in NZB/NZW F1 mice who spontaneously develop a lupus-like syndrome are being studied by a filter radioimmunoassay method. These antibodies develop earlier in female than in male NZB/NZW F1 mice. The females die earlier of lupus nephritis. We have studied the effects of neonatal thymectomy and prepubertal castration on antibodies to nucleic acids, nephritis and mortality in this animal model. We have evidence that androgens exert a protective influence, since castrated males develop a female pattern of disease expression. BIBLIOGRAPHIC REFERENCES: Talal, N., Pillarisetty, R., De Horatius, R.J. and Messner, R.P.: Immunologic regulation of spontaneous antibodies to DNA and RNA. I. Significance of IgM and IgG antibodies in SLE patients and asymptomatic relatives. Clin. Exp. Immuno., 25:377-383, 1976. Pillarisetty, J.R. and Talal, N.: Clinical studies of antibodies binding polyriboadenylic acid in systemic lupus erythematosus. Arth. and Rheum., 19:705-710, 1976.